With the progress in machine type communication (MTC), large numbers of MTC devices with small data transmission are used in various applications.
In Long Term Evolution (LTE) technology, a user equipment (UE) needs to perform a four-step random access procedure before data transmission. We applied contention-based non-orthogonal transmission to reduce the latency. This scheme allows devices to directly transmit data on the randomly selected resources. However, if the number of UE is large, data transmission may result in frequent collisions that deteriorate the system performance. Even worse, the retransmitted data may collide again with each other or with other newly transmitted data.